The Association of American Railroads (AAR) is an organization that oversees North American rail networks and sets new standards for innovation, safety, and technology in the rail industry. Changes to the AAR standard regulating the design of Automatic Engine Shutdown and Start devices (S-5502) have been contemplated and proposed. Such changes would dictate that all systems installed after Jul. 1, 2009 adopt new shutdown and restart algorithms accounting for the locomotive being in either the trail or lead position. The intent would be to allow the locomotive to stay shutdown for longer periods of time if it is, e.g., in a yard and in trail position and simply being moved by a lead locomotive.
Locomotives less than 10 years old and being built today will typically be equipped with electronic air brakes (EAB) from which the lead/trail status of the locomotive can be acquired through the air brake's communication port, which is continuously being monitored by the locomotive's controlling computer.
However, older locomotives and their completely pneumatic air brake controls do not have that capability. One option for dealing with the older locomotives, which has been discussed in the industry, includes measuring the pressure of the locomotive's equalizing reservoir, which should always read zero (0) PSI (i.e. exhausted to atmosphere) when the locomotive is in the trail position. When the locomotive is not in the trail position, equalizing reservoir pressure is controlled by the brake handle and while it should only go to zero (0) in the event of an emergency brake application, it may get close. This has the potential to cause an erroneous reading based on the sensing application, its accuracy, and its measurement hysteresis.
Therefore, there exists a need to accurately and consistently determine whether a locomotive in a consist is in leading mode or trailing mode.